Means for improving contact operation



Oct. 17, 1933. R, B SHANCK 1,930,627

MEANS FOR IMPROVING CONTACT OPERATION Filed Feb. 16, 1952 Patented Oct. 17, 1933 `UNITED STATES PATENT oFFIcE- MEANS FOR IMPROVING CONTACT OPERATION- Roy B. Shanck, Douglas Manor, N. Y., assigner to American Telephone and' Telegraph Company, a corporation of New York A Application February 16, 1932. Serial Nrn-593,348

7 Claims.

VThis invention relates to'electrical transmis-` sion systems, and more particularly to means for improving the transmission of' currents over such systems, when `such currents are transmittedv over the contacts of relays, switches or similar l5 example, arise in carrier telegraph systems andl in echo suppressor devices for short circuiting lines carrying small currents. The arrangements ofthe invention provide means for applying a comparatively high voltage across the contact pointsof the switching device, in order to break down the high contact resistance, in such a way that through transmission is not affected.

Further objects and Vfeatures. -of the invention will appear moreY fully from the detailed description Vthereof hereinafter given.

The invention may be more fully lunderstood from the following description together with the accompanying drawing, in theFigures l, 2, 3 and 4 of which the invention is illustrated. Fig. 1 is a circuit diagram illustarting the arrangements of the invention applied to a set of contacts connected in shunt across a transmissionline. Figs.

2 and 3 are modifications of the arrangements of Fig.` l. Fig. 4 is a circuit diagram'illustrating the arrangements of the invention applied to a set of contacts connected in series in a transmission line. Similar reference characters have been utilized to denote like parts in all of the figures.

In Fig. l vis shown a transmission line L connected to a sourceof current, such as the generator G. "Bridged kacross the line L would be a circuit arrangement including the switch K. When the contacts of switch K are open, current from'G will kow out over the line L. When switch K is closed, a shunt will be closed across the line L and substantially no current will flow out thereover, as will be pointed out hereinafter. An arrangement having the above characteristics might be utilized for the transmission of signals in a carrier telegraph system. For example, the arrangements of the invention might be applied to a carrier telegraph system of the type shown in U. S. Patent 1,773,789, issued rAugust 26, 1930 to W. T. Rea. This patent-shows a car- (Cl. ris- 66) rier telegraph sending Ycircuits 4 which might correspond to line L. An oscillator 5, which might. correspond to oscillator G, is connected to line 4 and adapted to beshort-circuited'by the .con-

tacts of relay 2. The arrangements of this invention. might be utilized to short-circuit line 4 in place of the relay contacts shown in the above mentioned patent. If comparatively small currents and voltages were carried bythe contacts of switch K trouble in the transmission of currents might be experienced due to the existence at such div contacts of a high resistance." Accordingly, the switch K is connected across line L by a balanced rectifier circuit-as shown.k Thisy circuit would include the rectiers R1, R2', R3 and 70" R4, poled as shown. "The requirement .for perfect balance is that the impedances of R1 and R2 be equal and-the impedance of Rgequal that of R4. A battery B poles as shown and acurrentlimiting resistance r shunted by a condenser. C 75. are connected as shown to one ofthe 'contacts of key K. It will be seen that with the switch 4K open, current will now freely fromthe generator G to the line L, the rectiersbeinff so poled'that no Vpathisbifered. throughthe bridgedl circuits. 80. When-the key K is closed, current will flow from the generator G through'rectiers R1 andRl-for one half of the alternating ycurrent wave v'and through rectiiiers R2 and R3 during'the other half, so that' substantially no current will liow` to the 85 line L. The condenser C is shown connected so as to effectively short circuit the current-limiting resistance r for alternating currents, vbut with a comparatively lowvalue of rthis .might not be necessary. In accordance with the arrangements of the invention the battery B provides a voltage across the contacts of switch K which will be effective in breaking down the resistance of a iilm or particles of dirt which may be upon the contacts. There is, however, no tendency for current from B to enter the line L or the generator G other than longitudinallydue to the fact that the' rectiers are balanced.y It might be desirable to isolate the rectiner arrangement by means of the transformer T2 to prevent' the `flow of current from the battery longitudinally through admittance to ground. Atransformer T1 is also desirable between the generator and the rectifier circuit because it is common practice to ground one terminal of the generator.V The battery may also be groun'dedas shown and be common to a number of circuits. g

In Fig. 2 Yis shown a modification of the arrangements of Fig. l. In Fig. 2 the current limiting resistance `is divided into two equal parts 1" and r", which are connected serially in the line. No condenser is needed in this case and the transformer T1 is omitted. In other respects the operation is similar to that heretofore described.

In Fig. 3 is shown a further modification of the arrangements of the invention. In this arrangement only two rectiers, R1 and R2, are

needed, but it is required that they be of a type,

the impedance of which for small superposed alternating currents becomes small when the rectified current becomes large. These rectiers are poled to oppose Veach other so as to oiTer no path for the current from the generator when the switch K is open. Bridged around these rectifiers, or across the line, is a circuit including the current limiting resistances r and 1', the batteries B1 and B2, and the inductances L1 and L2. This circuit arrangement will offer substantially no path for the current fromA generator G, when switch K is open, because of the impedance offered by inductances L1 and L2. Accordingly, when Vswitch K is open, current from generator G will be transmitted out over'the line L. When' switch K is closed current will flow from G for either half of the alternating current wave over the following path; from the tip side of the line through R1 and Rz to the ring side of the line. This is because the rectiers, as heretofore pointed out, are of the type in which the impedance for small superposed alternating currents decreases rapidly when the rectified current becomes large. When switch K is closl the voltages of the two batteries B1 and B2 are effective breaking down resistance existing across the contact points of switch K.

In Fig. 4 the arrangements of the invention are shown -applied -to the contacts of a switching device connected in series in a line rather than in shuntacross aline as in the previously described arrangements.V In this arrangement a balanced rectifier circuit is provided including rectiers R1, RzyRa and R4. The requirements for perfect balancev is that thev `impedances of R1 and R2 be equal and the impedance of R3 equal that of R4.:` Rectifiers R1 and R2 are oppositely poled and are connected serially, in the` line. Rectifiers Rsiand R4 are poled'oppositely vto each other and with respect to R1 and Rz, and connected serially in the line. The two sets of rectifiers are in parallel with each other. Connected between the rectifiers of each set is the battery B, the currentlimiting resistance r shunted by condenser C, and the switch K. The operation of the arrangements of Fig. 4 is the reverse of the previously described arrangements in that current flows over the line L when the switch K is closed and not when it is open. When the switch K is open the poling of the rectifiers will in effect open the line. Y When switchl K is closed a path for one half of the alternating current wave will be presented as follows; from the tip side of the line through R1, battery B, condenser C, switch K, rectier R4, to the ring side of the line. A path forthe other half of the alternating current wave will would be those of the copper-oxide variety. However, other types of rectiers may also be used.

Furthermore, while the generator G has been shown as of the alternating current variety, neverthless the arrangments of the invention are applicable to circuits utilizing sources of potential of other types, such for example as a battery. v V

While the arrangements of the invention have been disclosed as embodied in certain specific forms which are deemed desirable, it is understood that they are capable of embodiment in many and other widely varied forms without departing from the spirit of the invention as defined by the appended claims.

What is claimed is: i 1. An electrical circuit, a source of voltage connected thereto, a switching device having a set of contactsconnected to said circuit for controlling the ow of current over said circuit from said source of Voltage, and auxiliary means for applying a voltage across the contacts of said switching device to break down. the contact resistance thereof. f

2. An electrical circuit, a source of voltage connected thereto, and a switching device connected to said circuit for controlling the flow of current over said circuit from said source of voltage, said switching device comprisingv a circuit arrangement comprising two sets of rectiflers connected across said circuit, the rectifiers of each set being oppositely poled, and a. circuit `connected between the two sets of rectifiers and including the contacts of a switch and means for applying a voltage across said contacts.

; 3. An electrical circuit, a source of voltage connected thereto, and a switching device connected to said circuit for controlling the flow of current over said circuit from said source of voltage, said switching device comprising a circuit arrangement comprising two sets of rectiers, each set being connected to saidelectrical circuit and in parallel with the other set, the rectifiers of each set being oppositely poled with respect to each other and with the corresponding rectifiers in the other set, and a circuit connected from a point between the rectiersof one set to' a point between the 120 rectifiersof the other set, said circuit including the contacts of a switch and a source of voltage.

4. A transmission line, a source of voltage connected thereto, and a switching device connected to said line for controlling the flow of current over said line from said source of voltage, said switching device comprising a circuit arrangement comprising two sets of rectiiiers, each set being connectedto the line and in parallel with the other set, the rectiflers of each set being oppositely-poled with respect toY each other and with the corresponding'rectiers in the other set, the impedances of the rectiers in each set being equal to each other, and a circuit connected from a point between the rectifiers of one set to a point between the rectifiers of the other set, said circuit including the contacts of a switch, a current limiting resistance shunted by a condenser, and a source of voltage.

5. An electrical circuit, a source of voltage connected thereto, and a switching device connected to said circuit for controlling the ilow of current over said circuit from said source of voltage, said switching device comprising a circuit arrangement comprising two paths connected to 145 said electrical circuit andarranged for transmission in opposite directions, each of said paths having a portion thereof in common with the other, said common portion including the contacts of a switch and a source of voltage.

6. An electrical circuit, a source of voltage connected thereto, and a switching device connected to said circuit for controlling the flow of current over said circuit from said source of voltage, said switching device comprising a circuit connected across said electrical circuit including two oppositely poled rectiers, a second circuit connected across said electrical circuit inluding two inductances and two oppositely poled sources of voltage, and a circuit including the contacts of a- 

